Molecular Intercalation Regulation of Solid-State Reaction Enables Thermally Evaporated FASnI3 Light-Emitting Diodes

Tin-based perovskite light-emitting diodes (PeLEDs), particularly FASnI3-based devices, are promising for lead-free near-infrared optoelectronics. However, thermally evaporated FASnI3-PeLEDs remain unexplored because of the difficulty in controlling solid-state precursor diffusion, reaction, and crystallization. Here, we develop a molecular intercalation strategy to regulate the solid-state reaction and crystallization of layer-by-layer evaporated FASnI3. A tryptophan (Trp) interlayer modulates interfacial reaction kinetics and precursor interdiffusion, enabling controlled crystallization and improved structural quality. Meanwhile, Trp interacts strongly with the Sn-based perovskite lattice, suppressing defect formation and Sn2+ oxidation and thereby reducing nonradiative recombination. The resulting fully thermally evaporated FASnI3-PeLEDs achieve a peak radiance exceeding 100 W sr-1 m-2. Large-area devices up to 2500 mm2 and patterned devices with uniform emission are also demonstrated, highlighting the potential of molecularly regulated solid-state crystallization for scalable vacuum-processed perovskite optoelectronics.